1. Field of the Invention
The present invention relates to a semiconductor light-emitting element in which a roughened surface region which suppresses internal reflection of light is formed on a main ice of a semiconductor substrate from which light is taken out, and a manufacturing method thereof.
2. Description of the Related Art
The brightness is increased by forming a roughened surface which suppresses internal reflection of light on a main surface of a semiconductor light emitting element from which light is taken out (See Patent Document 1, for example).
FIG. 3 shows an example thereof. This semiconductor light-emitting element (light-emitting diode) includes an AlGaAs semiconductor substrate 3, for example, composed of a P-type semiconductor region 1 and an N-type semiconductor region 2, a P-side electrode 4, and at least one of N-side electrodes 5. A PN junction 6 at an interface between the P-type semiconductor region 1 and the N-type semiconductor region 2 extends parallel to one and the other main surfaces 3a and 3b of the semiconductor substrate 3.
The P-side electrode 4 is placed in one main surface (upper surface) 3a of the semiconductor substrate 3, in a central portion thereof for example, and connected to the P-type semiconductor region 1. At least one of the N-side electrodes 5 is formed in a lattice pattern or in a dot pattern, for example, and connected to the other main surface (lower surface) 3b of the semiconductor substrate 3, that is, to the N-type semiconductor region 2. The formation of at least one of the N-side electrodes 5 in a lattice pattern or in a dot pattern as described above makes it possible to efficiently reflect light, which is emitted from the PN junction 6 and heads for the lower surface, toward the upper surface in portions where no N-side electrode 5 is provided.
Light is taken out from the semiconductor light-emitting element in FIG. 3 in a direction toward the upper surface, and light emitted upward from the PN junction 6 out of the light to be taken out is taken out from a region of the upper surface of the semiconductor substrate 3 where the P-side electrode 4 is not formed. In this semiconductor light-emitting element, the region of the upper surface of the semiconductor substrate 3 from which the light is taken out is a roughened surface (minutely uneven surface, roughened surface region) 7. This roughened surface 7 is provided so as to reduce the probability of total reflection of the light emitted from the PN junction 6 to take out the light to the outside satisfactorily, thereby realizing higher brightness. This roughened surface 7 is formed by selectively forming the P-side electrode 4 almost at the center of the upper surface of the semiconductor substrate 3 and thereafter subjecting the upper surface of the semiconductor substrate 3 to etching (chemical treatment) or the like.
Incidentally, when such a semiconductor light-emitting element is formed as described above there sometimes occurs so-called over-etching (also called side-etching) in which etching progresses as far as a peripheral lower portion of the P-side electrode 4 as shown in FIG. 4 at the time of etching for forming the roughened surface after the electrode is formed. If such over-etching occurs, adhesion of a peripheral portion of the P-side electrode 4 to the semiconductor substrate 3 lowers, involving the problem such that the electrode peels off due to stress when resin molding or wire bonding is performed on the semiconductor light-emitting element, which has an influence upon the reliability of the electrode.
Hence, in an art described in Patent Document 1, as shown in FIG. 5, in order to inhibit the lowering of the adhesion of the peripheral portion of the P-side electrode 4 to the semiconductor substrate 3, a mirror surface 8 and the roughened surface 7 are formed in advance on the upper surface of the P-type semiconductor region 1 of the semiconductor light-emitting element, and when the P-side electrode 4 is formed on the mirror surface 8, the peripheral portion of the P-side electrode 4 is formed so as to partially cover the roughened surface 7, thus increasing the adhesion of the peripheral portion of the P-side electrode 4 to the semiconductor substrate 3 is realized.
(Patent Document 1)
Japanese Patent Laid-open No. Hei 10-200162
In the art described in Patent Document 1, electrode adhesion is increased by previously performing a surface roughening treatment to increase the brightness of the semiconductor light-emitting element in a range extending to a peripheral lower portion of a place where the electrode is formed and thereafter forming the P-side electrode 4 in such a manner that the peripheral portion thereof covers the roughened surface 7. Namely, the surface roughening treatment is performed in a stage prior to an electrode forming process. Therefore, a conventional order of steps in which the surface roughening treatment is performed after the electrode forming process needs to be greatly changed, which causes a problem that the burden of changing the steps is large.